Sample showing basic usage of Akka TestKit and TestActorRef

ImplicitSenderTest.scala

package sample.akka.testkit

import akka.actor.ActorSystem
import akka.actor.Actor
import akka.testkit.{TestKit, TestActorRef}
import org.scalatest.matchers.MustMatchers
import org.scalatest.WordSpec

class ImplicitSenderTest extends TestKit(ActorSystem("testSystem"))
  // Using the ImplicitSender trait will automatically set `testActor` as the sender
  with ImplicitSender
  with WordSpec
  with MustMatchers {

  "A simple actor" must {
    "send back a result" in {
      // Creation of the TestActorRef
      val actorRef = TestActorRef[SimpleActor]
      actorRef ! "akka"
      // This method assert that the `testActor` has received a specific message
      expectMsg("Hello akka")
    }

  }
}

SimpleTest.scala

package sample.akka.testkit

import akka.actor.ActorSystem
import akka.actor.Actor
import akka.testkit.{TestKit, TestActorRef}
import org.scalatest.matchers.MustMatchers
import org.scalatest.WordSpec

// Just a simple actor
class SimpleActor extends Actor {

  // Sample actor internal state
  var lastMsg: String = ""

  def receive = {
    case msg: String => {
      // Storing the message in the internal state variable
      lastMsg = msg
      sender ! "Hello " + msg
    }
  }
}

class SimpleTest extends TestKit(ActorSystem("testSystem"))
  with WordSpec
  with MustMatchers {

  "A simple actor" must {
    // Creation of the TestActorRef
    val actorRef = TestActorRef[SimpleActor]

    "receive messages" in {
      // This call is synchronous. The actor receive() method will be called in the current thread
      actorRef ! "world"
      // With actorRef.underlyingActor, we can access the SimpleActor instance created by Akka
      actorRef.underlyingActor.lastMsg must equal("world")
    }
  }
}